Expert Tips for Threat and Vulnerability Management with EPSS and SSVC

Threat and vulnerability management has become a critical task for organizations of all sizes. Traditional methods of prioritizing vulnerabilities based solely on CVSS scores are no longer sufficient to address the complex landscape of modern cyber threats. To tackle this challenge, two innovative frameworks have emerged: the Exploit Prediction Scoring System (EPSS) and the Stakeholder-Specific Vulnerability Categorization (SSVC).

These frameworks offer a more nuanced approach to vulnerability assessment and risk management. EPSS uses machine learning algorithms to predict the likelihood of a vulnerability being exploited in the wild, while SSVC takes into account the specific needs and contexts of different stakeholders. In this article, you’ll learn how to use these tools to improve your vulnerability prioritization process, make data-driven decisions, and allocate your resources more effectively. We’ll also explore practical tips for implementing EPSS and SSVC in your organization’s security strategy.

Understanding EPSS and SSVC Frameworks

What is EPSS?

The Exploit Prediction Scoring System (EPSS) is a data-driven framework that assesses vulnerabilities based on their potential for exploitation. It calculates a probability score between 0 and 1 (0% to 100%) for each vulnerability, indicating how likely it is to be exploited in the near future ¹. EPSS uses machine learning to analyze various factors contributing to a vulnerability’s exploitability, including attack complexity, discovery likelihood, potential impact, and the current threat landscape ¹.

EPSS, managed by the Forum of Incident Response and Security Teams (FIRST), merges descriptive data about vulnerabilities from the Common Vulnerabilities and Exposures (CVE) system with real-world exploitation evidence and community insights ¹. This approach enables EPSS to provide accurate and timely predictions regarding the likelihood of a vulnerability being exploited in the wild ¹.

One key feature of EPSS is its daily updates, which reflect new data as it emerges ². This ensures that you have access to the most current threat information when prioritizing vulnerability remediation efforts.

Key features of SSVC

The Stakeholder-Specific Vulnerability Categorization (SSVC) system, developed by Carnegie Mellon University’s Software Engineering Institute (SEI) in collaboration with CISA, offers a more nuanced approach to vulnerability assessment ³. SSVC improves upon the Common Vulnerability Scoring System (CVSS) by considering the impact of an exploit on a specific organization rather than just focusing on the technical severity of the vulnerability ⁴.

Key features of SSVC include:

1. Holistic scoring approach: SSVC assigns scores using five values: exploitation status, technical impact, automatability, mission prevalence, and public well-being impact ⁴.
2. Action-oriented categorization: SSVC categorizes vulnerabilities into four groups: Track, Track*, Attend, and Act ⁴. This categorization provides clear guidance on how to respond to identified vulnerabilities.
3. Stakeholder-specific assessment: SSVC takes into account the specific needs and contexts of different stakeholders, allowing for more tailored risk assessments ⁴.
4. Decision tree model: SSVC uses a decision tree to evaluate vulnerabilities, considering factors such as exploit existence, automatability, technical impact, mission impact, and well-being impact ⁴.

Comparing EPSS and SSVC

While both EPSS and SSVC aim to improve vulnerability prioritization, they have distinct approaches and strengths:

EPSS excels at predicting the likelihood of exploitation but lacks customization options and impact assessment capabilities ². SSVC, on the other hand, offers a more comprehensive approach by considering organizational context and providing actionable guidance ⁴.

To leverage the strengths of both systems, you might consider using EPSS for initial prioritization based on exploitation likelihood, followed by SSVC for a more nuanced, stakeholder-specific assessment. This combined approach can help you make more informed decisions about vulnerability management and resource allocation in your organization.

Implementing EPSS for Vulnerability Prioritization

Setting up EPSS scoring

To implement EPSS for vulnerability prioritization, you need to understand its scoring system. EPSS scores range from 0 to 1 (0% to 100%), indicating the probability of a vulnerability being exploited within the next 30 days ⁵. The higher the score, the greater the likelihood of exploitation ⁶. EPSS also provides percentile rankings, which measure the probability relative to all other EPSS scores, enabling advanced prioritization inputs ⁵.

To set up EPSS scoring, you have several options:

1. Use an SCA (software composition analysis) tool that incorporates EPSS scores
2. Download scores directly from the EPSS website as a CSV file
3. Utilize the EPSS API for integration into your existing systems ⁵

Integrating EPSS with existing tools

To effectively use EPSS, integrate it with your current vulnerability management tools. Many modern security platforms now support EPSS or allow for custom integrations using APIs ⁷. For example, if you’re using Prisma Cloud, you can access EPSS scores in the Vulnerability Management Dashboard, Search and Investigate Graph, and Common Vulnerabilities and Exposures (CVE) side panel ⁷.

When integrating EPSS, consider combining it with other metrics like CVSS. While CVSS provides severity ratings, EPSS adds the dimension of exploit likelihood ⁷. This combination offers a more comprehensive view of vulnerability risk.

Best practices for EPSS-based prioritization

To maximize the benefits of EPSS in your vulnerability management strategy:

1. Focus on internet-facing vulnerabilities: Prioritize vulnerabilities with higher EPSS scores that are reachable from the internet ⁷.
2. Create a risk-based remediation plan: Direct patching efforts toward vulnerabilities with high exploitation probabilities as indicated by EPSS ⁷.
3. Regularly review and adjust: Since FIRST updates EPSS scores frequently based on incoming data, monitor your dashboard for the latest scores ⁷.
4. Train your security team: Ensure your team understands how to interpret EPSS scores and integrate them into their daily workflow ⁷.
5. Use EPSS in conjunction with other data: While EPSS is valuable, it shouldn’t be the sole indicator of cyber risk. Combine it with other vulnerability management tools, threat intelligence sources, and risk assessment frameworks for a holistic understanding of your cyber risk posture ⁸.
6. Prioritize based on both severity and probability: Focus on vulnerabilities that have both high severity (as indicated by CVSS) and high probability of exploitation (as shown by EPSS) ⁸.

Remember, EPSS is most effective when there’s no other evidence of active exploitation. If concrete evidence of exploitation exists, that information should take precedence over EPSS scores ⁸. By implementing these practices, you can significantly enhance your vulnerability management strategy and allocate resources more effectively to address the most critical threats.

Leveraging SSVC for Stakeholder-Specific Risk Assessment

To effectively leverage the Stakeholder-Specific Vulnerability Categorization (SSVC) framework for risk assessment, you need to understand its core principles and implementation strategies. SSVC improves upon the Common Vulnerability Scoring System (CVSS) by considering the impact of an exploit on your specific organization, rather than just focusing on the technical severity of the vulnerability ⁴. This approach equips you with the information needed to evaluate how remediation should be handled within your unique environment.

Creating SSVC decision trees

SSVC utilizes decision trees to systematically evaluate the severity and impact of vulnerabilities. These trees guide your decision-making process by assessing vulnerabilities against a series of criteria tailored to your organization’s specific context ⁹. To create an effective SSVC decision tree:

1. Define decision points: Identify factors that influence vulnerability prioritization, such as exploitation status, technical impact, automatability, mission prevalence, and public well-being impact ⁴.
2. Establish outcomes: Determine the possible results of your decision-making process. SSVC typically categorizes vulnerabilities into four groups: Track, Track*, Attend, and Act ⁴.
3. Develop a policy: Create a mapping from each combination of decision point values to the set of outcome values ¹⁰.
4. Incorporate relevant data sources: Utilize information from CVSS vectors and Exploit Prediction Scoring System (EPSS) to inform decision points like Technical Impact and Exploitation ¹⁰.

Customizing SSVC for your organization

To tailor SSVC to your organization’s needs:

1. Assess asset inventory and importance: Agree on your asset inventory and the relative importance of each asset ⁴.
2. Identify existing vulnerabilities: Conduct thorough scans of your environment’s software and hardware assets to determine what vulnerabilities exist ⁴.
3. Define impact criteria: Determine how different types of attacks could affect your organization. For example, consider whether a spoofing attack is more likely to compromise customer information or internal user credentials with elevated privileges ⁴.
4. Integrate with existing tools: Ensure that SSVC is integrated with all internal and external sources of vulnerability management to maintain consistency across your organization ⁴.
5. Automate the process: Implement rules for automating prioritization decisions based on your defined criteria. This can be done using platforms like Nucleus Security, which allows you to set up decision trees and rules to automate vulnerability evaluation ⁹.

SSVC implementation challenges and solutions

Implementing SSVC can present several challenges:

1. Complexity: SSVC requires a more nuanced approach than traditional CVSS scoring. To address this, start with a basic setup using as few as 16 rules and gradually increase granularity as needed ⁹.
2. Data integration: Gathering the necessary context for decision-making can be challenging. Utilize platforms that can integrate and normalize data from various sources, such as security detection tools, IT service management platforms, and cloud service provider APIs ¹¹.
3. Cross-team collaboration: SSVC requires input from various stakeholders. Encourage collaboration between different teams and align SSVC implementation with DevSecOps principles ⁹.
4. Continuous updates: Vulnerability management is an ongoing process. Implement a system for tracking the lifecycle of vulnerabilities and regularly updating your SSVC model based on new threat intelligence ⁴.

By addressing these challenges and customizing SSVC to your organization’s needs, you can significantly improve your vulnerability prioritization process and allocate resources more effectively to address the most critical threats.

Conclusion

EPSS and SSVC offer powerful tools to enhance vulnerability management strategies. EPSS provides data-driven insights into exploitation likelihood, while SSVC allows for tailored risk assessments based on organizational context. By integrating these frameworks, security teams can prioritize vulnerabilities more effectively, allocating resources to address the most critical threats first.

To implement these frameworks successfully, organizations should focus on integrating EPSS and SSVC with existing tools, creating custom decision trees, and fostering cross-team collaboration. Regular updates and continuous monitoring are crucial to maintain an effective vulnerability management process. This approach enables organizations to stay ahead of emerging threats and make informed decisions about vulnerability remediation.

FAQs

What are the key stages involved in managing vulnerabilities? The vulnerability management process includes several critical stages:

• Stage 0: Planning and initial preparations.
• Stage 1: Discovering assets and assessing vulnerabilities.
• Stage 2: Prioritizing vulnerabilities.
• Stage 3: Resolving vulnerabilities.
• Stage 4: Verifying and monitoring the effectiveness of resolutions.
• Stage 5: Reporting outcomes and refining processes.

How do SSVC and EPSS differ in managing vulnerabilities? SSVC (Stakeholder-Specific Vulnerability Categorization) primarily focuses on the current exploitation status of a vulnerability, without predicting future exploit probabilities. In contrast, EPSS (Exploit Prediction Scoring System) provides an estimate on the likelihood of a vulnerability being exploited in the short term, based on available data.

What are the main phases of a vulnerability management program? Vulnerability management typically involves four main phases:

1. Identification of security vulnerabilities in systems and software.
2. Evaluation of these vulnerabilities to understand their potential impact.
3. Mitigation of risks through appropriate measures.
4. Reporting the findings and actions taken.

What is considered the most effective strategy for managing vulnerabilities? An effective vulnerability management strategy should encompass the following best practices:

• Discovering vulnerabilities.
• Prioritizing vulnerabilities based on their severity and impact.
• Remedying identified vulnerabilities.
• Validating the effectiveness of the remediation.
• Reporting on the vulnerabilities and actions taken. Additionally, establishing a comprehensive vulnerability management program and securing cloud-native applications with holistic oversight are recommended.

References

[1] – https://www.brinqa.com/glossary/what-is-epss-score/
[2] – https://www.endorlabs.com/learn/cve-vulnerability-epss-ssvc-reachability-vex
[3] – https://www.cisa.gov/stakeholder-specific-vulnerability-categorization-ssvc
[4] – https://www.silk.security/vulnerability-management-lifecycle/ssvc
[5] – https://fossa.com/blog/understanding-using-epss-scoring-system/
[6] – https://www.first.org/epss/
[7] – https://www.paloaltonetworks.com/blog/prisma-cloud/epss-scores/
[8] – https://vulcan.io/blog/thinking-of-using-epss-heres-what-you-need-to-know/
[9] – https://nucleussec.com/blog/5-things-to-consider-before-using-ssvc-to-automate-vulnerability-prioritization/
[10] – https://certcc.github.io/SSVC/tutorials/
[11] – https://www.silk.security/blog/ssvc-meets-the-real-world-making-risk-resolution-practical